linux-kernel - Re: [PATCH] mm,page_alloc: PF_WQ_WORKER threads must sleep at should_reclaim

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Date:   Tue, 31 Jul 2018 06:01:48 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Michal Hocko <mhocko@...nel.org>, Tejun Heo <tj@...nel.org>
Cc:     Roman Gushchin <guro@...com>, Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm,page_alloc: PF_WQ_WORKER threads must sleep at
 should_reclaim_retry().

On 2018/07/31 4:10, Michal Hocko wrote:
> Since should_reclaim_retry() should be a natural reschedule point,
> let's do the short sleep for PF_WQ_WORKER threads unconditionally in
> order to guarantee that other pending work items are started. This will
> workaround this problem and it is less fragile than hunting down when
> the sleep is missed. E.g. we used to have a sleeping point in the oom
> path but this has been removed recently because it caused other issues.
> Having a single sleeping point is more robust.

linux.git has not removed the sleeping point in the OOM path yet. Since removing the
sleeping point in the OOM path can mitigate CVE-2016-10723, please do so immediately.
(And that change will conflict with Roman's cgroup aware OOM killer patchset. But it
should be easy to rebase.)